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Do I need BUS-powered USB hub or active-power USB hub?

Published On 05/27/2021 12:37 PM by QZ Support
It is important to assess if your USB devices' total current demand is met by the USB hub before purchase.
Yes. for better performance, the combined current demand by the connected USB devices should not exceed the output current of the USB hub. Otherwise, output current may become unstable or disconnect entirely.

For BUS-powered USB hubs (hubs without external power adapter): The current available is limited to the total power available from the host computer USB port. It is usually 0.9A at 5V for USB-A 3.0 port.
For external powered USB hubs (active USB hubs): The current available is limited to the output current of the USB hub. The output current of the USB hub is equal to the current supplied by the external power adapter provided with it. For example, if an active USB hub is supplied with 12V 3A power adapter, the total power available is 36W (12V x 3A). USB-A type connectors are supported at 5V. To know the total current available, divide the total power by 5V: 36W/5V = 7.2A. So, 7.2 A is the total current available in an USB hub supplied with 12V 3A power adapter.

Some commonly used USB devices' general requirements: 250G Hard drive – 600mA, 4G Flash drive – 100mA, 64G SSD – 400mA, 100M Network adapter – 500mA, Keyboards and mice and other peripheral devices – 100mA (or less)
The ratings above are estimates only; please check your specific device's actual ratings.

Make sure the total current output of the USB hub is higher than your demand before buying.
To generalise this, if the combined current demand by your USB devices is less than 0.9A at 5V, BUS-powered USB hub would suffice; else you need external powered USB hub. 
This entry was posted in Active-power USB hubs

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